As conventional, an information encrypting transmission and reception method is implemented by various proposed cryptosystems. The best known cryptosystems of those proposed systems is an RSA (Rirest-Shamir-Adleman). In the RSA, sender's information is encrypted in use of receiver's “public key” before transmitting, and also, the sender and the receiver transmit and receive their electronic signatures so that the receiver certifies the identification of the sender and the validity of the transmitted information. Such double processes are required in the RSA (for example, see Japanese patent applications laid-open No. H11-353280 and No. 2001-052125).